Punch presses, brakes, bending machines and other heavy machinery pose a great danger to the operator unless actuation of the device requires that both hands of the operator be withdrawn from the machinery before it can be actuated. Early mechanisms provided two spaced actuator buttons to occupy both hands of the operator away from the operating parts of the device while it was in operation. However, many of those prior art devices could be defeated by tying one button down, thus enabling the operator to actuate the machine with one hand. Two handed devices requiring simultaneous actuation to prevent the operator from tying down one of the buttons are disclosed in U.S. Pat. Nos. 2,046,531; 2,962,633; 3,491,867; 3,563,356; and 4,085,626. However, each of these mechanisms is in some respect unduly complex.